This book presents selected papers from the 12^th edition of the Spring School of Transition and Turbulence which took place in 2020. The papers cover applications on a number of industrial processes, such as the automotive, aeronautics, chemicals, oil and gas, food, nanotechnology, and others. The readers find out research and applied works on the topics of aerodynamics, computational fluid dynamics, instrumentation and experiments, multi-phase flows, and theoretical and analytical modeling.